The use of non-electric explosives initiation systems is now well known in the blasting art. Generally, these systems comprise the use of one or more lengths of detonating fuse cord each having attached at one end thereof an instantaneous or delay blasting cap. When the opposite end of the cord is initiated by means of an explosive initiator, such as a cap or priming trunk line fuse cord, the detonating fuse is detonated and an explosive wave is transmitted along its length at high velocity to set off the attached blasting cap. The use of such a system is generally chosen where there may be hazards involved in using an electric initiation system and electric blasting caps.
In the past, many improvements have been made in the quality and reliability of non-electric initiation systems and in detonating fuse cord. An early but significant development was disclosed in our British patent No 808 087 (equals U.S. Pat. No. 2 993 236) This provided a solution to the problem of how to safely incorporate an explosive core in a thermoplastic tubular sheath during extrusion. The technique disclosed therein can be widely applied to production of tubular products for use in initiation systems. One such product is shown in British Patent No. 1 238 503 (equals U.S. Pat. No. 3 590 739; CA 878 056) which discloses a detonating fuse which comprises a tube having only a thin layer of a reactive substance coated on the inner area thereof rather than a core. Such a fuse is marketed under the registered trade mark "NONEL". Commonly, this type of fuse has come to be known as a shock wave conductor and will be referred to as such hereinafter.
The production of shock wave conductors of small diameter has been restricted to use of a limited number of polymers due to the principal properties sought for the product. The product development trend in the art to meet such problems has been to provide laminated plastics tubes comprising an inner and outer layer of differing plastics to satisfy requirements of reactive substance adhesion and mechanical strength respectively. A shock wave conductor in the form of a two-ply laminated tube, the outer ply of which provides reinforcement and resists mechanical damage, is disclosed in GB 2 027 176 (U.S. Pat. No. 4 328 753; CA 1 149 229). Likewise in U.S. Pat. No. 4 607 573, a method is described for the manufacture of a two-ply or multiply shock tube wherein the outer covering is applied only after the inner tube has been stretched to provide the desired core load per unit length. Further examples of such over coated tubes are disclosed in U.S. Pat. No. 4 757 764 which proposes use of the tubes of the type disclosed in the above-mentioned U.S. Pat. No. 4 607 573 with non-self-explosive reactive material within the tube. Other disclosures of the use of non-self-explosive reactive material are to be found in Brazilian Patent No. PI 8104552, CA 878 056, GB 2 152 643 and U.S. Pat. Nos. 4 660 474 and 4 756 250.
While the invention of the shock wave conductor has been an important contribution to the art of blasting, the known shock wave conductors are not without disadvantages. Since the reactive substance within the tube only comprises a thin surface coating which adheres to, but is not bound to the tube, then only certain special plastics have in practice been found suitable to provide the necessary adhesion. Such special plastics tend to be both expensive and to lack mechanical strength. When protected by an outer layer of material, as disclosed in U.S. Pat. Nos. 4 328 753 and 4 607 573, the mechanical properties are improved.